In the present state of technology the devices previously mentioned are known, for example, from GB-PS 1,058,894, in which dirt is sucked out and carried away by means of a suction channel from the fleece lying on the main cylinder after the passage of the revolving flat by means of a knife arranged opposite to the direction of rotation of the main cylinder. A fleece guiding deflector is introduced to the knife, seen in the direction of rotation of the main cylinder.
An improved embodiment of the previously mentioned device for the elimination of dirt, also called briefly "dirt separator", is shown in DE-3,034,036 C2 (equivalent to U.S. Pat. No. 4,400,852) in which an additional saw toothed clothing is provided directly after the knife, in order to lay the fibre layer on the main cylinder so that the fibres are again laid parallel after they had been brought into a certain random layer by the suction.
A further dirt separator is shown in U.S. Pat. No. 4,309,796, in which the guide plate introduced to the knife is subsequently arranged seen in the direction of rotation of the main cylinder and a static carding element is provided directly after the knife. The whole is shown in a carding machine in which only static carding elements are used and a dirt separator previously mentioned is provided between these static elements, respectively.
A similar embodiment is shown in DE-2,846,109 C3 (equivalent to U.S. Pat. No. 4,314,387) in which, likewise after a static carding element, (seen in the direction of rotation of the main cylinder) a guide plate is provided opposite to the surface of the main cylinder as well as a knife which forms a specified separation gap and which is fastened on the subsequent static carding element.
Thereby the guide surface is part of a collecting rail which is adjustable away from and against the main cylinder surface, as also applies to the guide knife.
Moreover, the latter elements are still adjustable in such a way that the clearance of the separation gap between the edge of the knife and the collecting rail is alterable.
The general disadvantage of the previously mentioned state of technology can be observed in the opening room and card room from the viewpoint of the development of the throughput performance of modern machines, in that the performance in these areas has considerably increased in latter years.
In particular, not only higher throughput performances are demanded from the cards, but also an improved carded sliver, so that development work must be undertaken in the systematics of the individual carding functions in order to obtain a more even carded sliver with higher performance, which, moreover, has less neps, dirt content and less damage to the fibers.
In the previously mentioned state of technology it can be established without exception that the inventors at this stage of technological development were of the opinion that, before reaching the edge of the knife previously mentioned, the fibre fleece lying on the main cylinder must be guided through a smooth guide surface, in order to obtain good results. This consideration emanated from the experience that a dirt separator gap between two static card elements without the guide surface previously mentioned shows a so-called "snout" in the separation gap which had the disadvantage that this snout, if uncontrolled, could reach either the suction or the fleece. This "snout-effect" could be eliminated with the previously mentioned guide plate introduced to the knife.
In the high performances demanded from such a card at the present time, it is, however, necessary not to have any surfaces on the main cylinder which do not have a carding function, if possible.
For this reason, the task is to find a substitute for the previously mentioned guide plate which has at least a positive carding result without the so-called snout effect.
Experiments have now surprisingly shown that a card rod turned through 180.degree., which is inserted instead of the previously mentioned guide surface, still gave a good carding result whilst guiding the fibres to the knife without the appearance of a snout.
For this reason, the invention solving this problem goes therefore, in the direction that the state of technology previously mentioned has attached the criterion that the preparatory element should have a structured surface opposite to the periphery of the toothed roller.